Magnetically shielded conductor

ABSTRACT

A magnetically shielded conductor assembly with a conductor device and a film of nanomagnetic material located above the conductor device. The conductor device has a resistivity of from about 1 to about 2,000 micro ohm-centimeters. The film of nanomagnetic material has a thickness of from about 100 nanometers to about 10 micrometers and a magnetic shielding factor of at least about 0.5. The nanomagnetic material has a mass density of at least about 0.01 grams per cubic centimeter, a saturation magnetization of from about 1 to about 36,000 Gauss, a coercive force of from about 0.01 to about 5,000 Oersteds, a relative magnetic permeability of from about 1 to about 500,000, and an average particle size of less than about 100 nanometers.

REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation-in-part of applicant's copendingpatent application U.S. Ser. No. 10/054,407, filed on Jan. 22, 2002 nowU.S. Pat. No. 6,506,972.

FIELD OF THE INVENTION

A conductor assembly comprised of a conductor device coated withnanomagnetic material,

BACKGROUND OF THE INVENTION

Many implanted medical devices that are powered by electrical energyhave been developed. Most of these devices comprise a power source, oneor more conductors, and a load.

When a patient with one of these implanted devices is subjected to highintensity magnetic fields, currents are often induced in the implantedconductors. The large current flows so induced often create substantialamounts of heat. Because living organisms can generally only survivewithin a relatively narrow range of temperatures, these large currentflows are dangerous.

Furthermore, implantable devices, such as implantable pulse generators(IPGs) and cardioverter/ defibrillator/pacemaker (CDPs), are sensitiveto a variety of forms of electromagnetic interference (EMI). Thesedevices include sensing and logic systems that respond to low-levelsignals from the heart. Because the sensing systems and conductiveelements of these implantable devices are responsive to changes in localelectromagnetic fields, they are vulnerable to external sources ofsevere electromagnetic noise, and in particular to electromagneticfields emitted during magnetic resonance imaging (MRI) procedures.Therefore, patients with implantable devices are generally advised notto undergo magnetic resonance imaging (MRI) procedures, which oftengenerate magnetic fields of from between about 1 about 20 Teslas.

One additional problem with implanted conductors is that, when they areconducting electricity and are simultaneously subjected to largemagnetic fields, a Lorentz force is created which often causes theconductor to move. This movement may damage body tissue.

In U.S. Pat. No. 4,180,600, there is disclosed and claimed a finemagnetically shielded conductor wire consisting of a conductive coppercore and a magnetically soft alloy metallic sheath metallurgicallysecured to the conductive core, wherein the sheath consists essentiallyof from 2 to 5 weight percent of molybdenum, from about 15 to about 23weight percent of iron, and from about 75 to about 85 weight percent ofnickel. Although the device of this patent does provide magneticshielding, it still creates heat when it interacts with strong magneticfields.

It is an object of this invention to provide a conductor assembly, whichis shielded from large magnetic fields and which does not create largeamounts of heat in the presence of such fields.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a magneticallyshielded conductor assembly comprised of a conductor device and a filmof nanomagnetic material disposed above the conductor device. Theconductor device has a resistivity at 20 degrees Centigrade of fromabout 1 to about 2,000 micro ohm-centimeters and is comprised of a firstsurface exposed to electromagnetic radiation. The film of nanomagneticmaterial has a thickness of from about 100 nanometers to about 10micrometers and a magnetic shielding factor of at least about 0.5 and isdisposed above at least about 50 percent of the first surface exposed toelectromagnetic radiation. The nanomagnetic material has a mass densityof at least about 0.01 grams per cubic centimeter, a saturationmagnetization of from about 1 to about 36,000 Gauss, a coercive force offrom about 0.01 to about 5,000 Oersteds, a relative magneticpermeability of from about 1 to about 500,000, and an average particlesize of less than about 100 nanometers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to the following drawings,in which like numerals refer to like elements, and in which:

FIG. 1 is a schematic sectional view of a shielded implanted devicecomprised of one preferred conductor assembly of the invention;

FIG. 1A is a flow diagram of a preferred process of the invention;

FIG. 2 is an enlarged sectional view of a portion of the conductorassembly of FIG. 1;

FIG. 3 is a sectional view of another conductor assembly of thisinvention;

FIG. 4 is a schematic view of the conductor assembly of FIG. 2.;

FIG. 5 is a sectional view of the conductor assembly of FIG. 2;

FIG. 6 is a schematic of another preferred shielded conductor assembly;

FIG. 7 is a schematic of yet another configuration of a shieldedconductor assembly;

FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a substrate,such as one of the specific medical devices described in thisapplication, coated with nanomagnetic particulate matter on its exteriorsurface;

FIG. 9 is a schematic sectional view of an elongated cylinder, similarto the specific medical devices described in this application, coatedwith nanomagnetic particulate (the cylinder encloses a flexible,expandable helical member, which is also coated with nanomagneticparticulate material);

FIG. 10 is a flow diagram of a preferred process of the invention;

FIG. 11 is a schematic sectional view of a substrate, similar to thespecific medical devices described in this application, coated with twodifferent populations of elongated nanomagnetic particulate material;

FIG. 12 is a schematic sectional view of an elongated cylinder, similarto the specific medical devices described in this application, coatedwith nanomagnetic particulate, wherein the cylinder includes a channelfor active circulation of a heat dissipation fluid;

FIGS. 13A, 13B, and 13C are schematic views of an implantable cathetercoated with nanomagnetic particulate material;

FIGS. 14A through 14G are schematic views of an implantable, steerablecatheter coated with nanomagnetic particulate material;

FIGS. 15A, 15B and 15C are schematic views of an implantable guide wirecoated with nanomagnetic particulate material;

FIGS. 16A and 16B are schematic views of an implantable stent coatedwith nanomagnetic particulate material;

FIG. 17 is a schematic view of a biopsy probe coated with nanomagneticparticulate material; and

FIGS. 18A and 18B are schematic views of a tube of an endoscope coatedwith nanomagnetic particulate material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic sectional view of one preferred device 10 that, inone embodiment, is implanted in a living organism. Referring to FIG. 1,it will be seen that device 10 is comprised of a power source 12, afirst conductor 14, a second conductor 16, a first insulative shield 18disposed about power source 12, a second insulative shield 20 disposedabout a load 22, a third insulative shield 23 disposed about a firstconductor 14, and a second conductor 16, and a multiplicity ofnanomagnetic particles 24 disposed on said first insulative shield, saidsecond insulative shield, and said third insulative shield.

In the embodiment depicted in FIG. 1, the power source 12 is a battery12 that is operatively connected to a controller 26. In the embodimentdepicted, controller 26 is operatively connected to the load 22 and theswitch 28. Depending upon the information furnished to controller 26, itmay deliver no current, direct current, and/or current pulses to theload 22.

In one embodiment, not shown, the controller 26 and/or the wires 30 and32 are shielded from magnetic radiation. In another embodiment, notshown, one or more connections between the controller 26 and the switch28 and/or the load 22 are made by wireless means such as, e.g.,telemetry means.

In one embodiment, not shown, the power source 12 provides a source ofalternating current. In another embodiment, the power source 12 inconjunction with the controller 26 provides pulsed direct current.

The load 22 may be any of the implanted devices known to those skilledin the art. Thus, e.g., load 22 may be a pacemaker. Thus, e.g., load 22may be an artificial heart. Thus, e.g., load 22 may be a heart-massagingdevice. Thus, e.g., load 22 may be a defibrillator.

The conductors 14 and 16 may be any conductive material(s) that have aresistivity at 20 degrees Centigrade of from about 1 to about 2,000microohm-centimeters. Thus, e.g., the conductive material(s) may besilver, copper, aluminum, alloys thereof, mixtures thereof, and thelike.

In one embodiment, the conductors 14 and 16 consist essentially of suchconductive material. Thus, e.g., it is preferred not to use, e.g.,copper wire coated with enamel. The use of such typical enamel coatingon the conductor does not work well in the instant invention.

In the first step of the process of this invention, step 40, theconductive wires 14 and 16 are coated with electrically insulativematerial. Suitable insulative materials include nano-sized silicondioxide, aluminum oxide, cerium oxide, yttrium-stabilized zirconia,silicon carbide, silicon nitride, aluminum nitride, and the like. Ingeneral, these nano-sized particles will have a particle sizedistribution such that at least about 90 weight percent of the particleshave a maximum dimension in the range of from about 10 to about 100nanometers.

The coated conductors 14 and 16 may be prepared by conventional meanssuch as, e.g., the process described in U.S. Pat. No. 5,540,959, theentire disclosure of which is hereby incorporated by reference into thisspecification. This patent describes and claims a process for preparinga coated substrate, comprising the steps of: (a) creating mist particlesfrom a liquid, wherein: 1. said liquid is selected from the groupconsisting of a solution, a slurry, and mixtures thereof, 2. said liquidis comprised of solvent and from 0.1 to 75 grams of solid material perliter of solvent, 3. at least 95 volume percent of said mist particleshave a maximum dimension less than 100 microns, and 4. said mistparticles are created from said first liquid at a rate of from 0.1 to 30milliliters of liquid per minute; (b) contacting said mist particleswith a carrier gas at a pressure of from 761 to 810 millimeters ofmercury; (c) thereafter contacting said mist particles with alternatingcurrent radio frequency energy with a frequency of at least 1 megahertzand a power of at least 3 kilowatts while heating said mist particles toa temperature of at least about 100 degrees centigrade, therebyproducing a heated vapor; (d) depositing said heated vapor onto asubstrate, thereby producing a coated substrate; and (e) subjecting saidcoated substrate to a temperature of from about 450 to about 1,400degrees centigrade for at least about 10 minutes.

By way of further illustration, one may coat conductors 14 and 16 bymeans of the processes disclosed in a text by D. Satas on “CoatingsTechnology Handbook” (Marcel Dekker, Inc., New York, N.Y., 1991). As isdisclosed in such text, one may use cathodic arc plasma deposition (seepages 229 et seq.), chemical vapor deposition (see pages 257 et seq.),sol-gel coatings (see pages 655 et seq.), and the like.

FIG. 2 is a sectional view of the coated conductors 14/16 of the deviceof FIG. 1. Referring to FIG. 2, it will be seen that conductors 14 and16 are separated by insulating material 42. In order to obtain thestructure depicted in FIG. 2, one may simultaneously coat conductors 14and 16 with the insulating material so that such insulators both coatthe conductors 14 and 16 and fill in the distance between them withinsulation.

The insulating material 42 that is disposed between conductors 14/16,may be the same as the insulating material 44/46 that is disposed aboveconductor 14 and below conductor 16. Alternatively, and as dictated bythe choice of processing steps and materials, the insulating material 42may be different from the insulating material 44 and/or the insulatingmaterial 46. Thus, step 48 of the process describes disposing insulatingmaterial between the coated conductors 14 and 16. This step may be donesimultaneously with step 40; and it may be done thereafter.

The insulating material 42, the insulating material 44, and theinsulating material 46 each generally has a resistivity of from about1,000,000,000 to about 10,000,000,000,000 ohm-centimeters.

After the insulating material 42/44/46 has been deposited, and in oneembodiment, the coated conductor assembly is preferably heat treated instep 50. This heat treatment often is used in conjunction with coatingprocesses in which the heat is required to bond the insulative materialto the conductors 14/16.

The heat-treatment step may be conducted after the deposition of theinsulating material 42/44/46, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated conductors 14/16 to a temperature of from about 200 to about600 degrees Centigrade for from about 1 minute to about 10 minutes.

Referring again to FIG. 1A, and in step 52 of the process, after thecoated conductors 14/16 have been subjected to heat treatment step 50,they are allowed to cool to a temperature of from about 30 to about 100degrees Centigrade over a period of time of from about 3 to about 15minutes.

One need not invariably heat treat and/or cool. Thus, referring to FIG.1A, one may immediately coat nanomagnetic particles onto to the coatedconductors 14/16 in step 54 either after step 48 and/or after step 50and/or after step 52.

In step 54, nanomagnetic materials are coated onto the previously coatedconductors 14 and 16. This is best shown in FIG. 2, wherein thenanomagnetic particles are identified as particles 24.

In general, and as is known to those skilled in the art, nanomagneticmaterial is magnetic material which has an average particle size lessthan 100 nanometers and, preferably, in the range of from about 2 to 50nanometers. Reference may be had, e.g., to U.S. Pat. Nos. 5,889,091(rotationally free nanomagnetic material), 5,714,136, 5,667,924, and thelike. The entire disclosure of each of these United States patents ishereby incorporated by reference into this specification.

The nanomagnetic materials may be, e.g., nano-sized ferrites such as,e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No. 5,213,851,the entire disclosure of which is hereby incorporated by reference intothis specification. This patent claims a process for coating a layer offerritic material with a thickness of from about 0.1 to about 500microns onto a substrate at a deposition rate of from about 0.01 toabout 10 microns per minute per 35 square centimeters of substratesurface, comprising the steps of: (a) providing a solution comprised ofa first compound and a second compound, wherein said first compound isan iron compound and said second compound is selected from the groupconsisting of compounds of nickel, zinc, magnesium, strontium, barium,manganese, lithium, lanthanum, yttrium, scandium, samarium, europium,terbium, dysprosium, holmium, erbium, ytterbium, lutetium, cerium,praseodymium, thulium, neodymium, gadolinium, aluminum, iridium, lead,chromium, gallium, indium, chromium, samarium, cobalt, titanium, andmixtures thereof, and wherein said solution is comprised of from about0.01 to about 1,000 grams of a mixture consisting essentially of saidcompounds per liter of said solution; (b) subjecting said solution toultrasonic sound waves at a frequency in excess of 20,000 hertz, and toan atmospheric pressure of at least about 600 millimeters of mercury,thereby causing said solution to form into an aerosol; (c) providing aradio frequency plasma reactor comprised of a top section, a bottomsection, and a radio-frequency coil; (d) generating a hot plasma gaswithin said radio frequency plasma reactor, thereby producing a plasmaregion; (e) providing a flame region disposed above said top section ofsaid radio frequency plasma reactor; (f) contacting said aerosol withsaid hot plasma gas within said plasma reactor while subjecting saidaerosol to an atmospheric pressure of at least about 600 millimeters ofmercury and to a radio frequency alternating current at a frequency offrom about 100 kilohertz to about 30 megahertz, thereby forming a vapor;(g) providing a substrate disposed above said flame region; and (h)contacting said vapor with said substrate, thereby forming said layer offerritic material.

By way of further illustration, one may use the techniques described inan article by M. De Marco, X. W. Wang, et al. on “Mossbauer andmagnetization studies of nickel ferrites” published in the Journal ofApplied Physics 73(10), May 15, 1993, at pages 6287-6289.

In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated conductors 14/16 is less than about 5 micronsand generally from about 0.1 to about 3 microns.

After the nanomagnetic material is coated in step 54, the coatedassembly may be optionally heat-treated in step 56. In this optionalstep 56, it is preferred to subject the coated conductors 14/16 to atemperature of from about 200 to about 600 degrees Centigrade for fromabout 1 to about 10 minutes.

In one embodiment, illustrated in FIG. 3, one or more additionalinsulating layers 43 are coated onto the assembly depicted in FIG. 2, byone or more of the processes disclosed hereinabove. This is conducted inoptional step 58 (see FIG. 1A).

FIG. 4 is a partial schematic view of the assembly 11 of FIG. 2,illustrating the current flow in such assembly. Referring go FIG. 4, itwill be seen that current flows into conductor 14 in the direction ofarrow 60, and it flows out of conductor 16 in the direction of arrow 62.The net current flow through the assembly 11 is zero; and the netLorentz force in the assembly 11 is thus zero. Consequently, even highcurrent flows in the assembly 11 do not cause such assembly to move.

In the embodiment depicted in FIG. 4, conductors 14 and 16 aresubstantially parallel to each other. As will be apparent, without suchparallel orientation, there may be some net current and some net Lorentzeffect.

In the embodiment depicted in FIG. 4, and in one preferred aspectthereof, the conductors 14 and 16 preferably have the same diametersand/or the same compositions and/or the same length.

Referring again to FIG. 4, the nanomagnetic particles 24 are present ina density sufficient so as to provide shielding from magnetic flux lines64. Without wishing to be bound to any particular theory, applicantbelieves that the nanomagnetic particles 24 trap and pin the magneticlines of flux 64.

In order to function optimally, the nanomagnetic particles 24 have aspecified magnetization. As is known to those skilled in the art,magnetization is the magnetic moment per unit volume of a substance.Reference may be had, e.g., to U.S. Pat. Nos. 4,169,998, 4,168,481,4,166,263, 5,260,132, 4,778,714, and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

Referring again to FIG. 4, the layer of nanomagnetic particles 24preferably has a saturation magnetization, at 25 degrees Centigrade, offrom about 1 to about 36,000 Gauss, or higher. In one embodiment, thesaturation magnetization at room temperature of the nanomagneticparticles is from about 500 to about 10,000 Gauss. For a discussion ofthe saturation magnetization of various materials, reference may be had,e.g., to U.S. Pat. Nos. 4,705,613, 4,631,613, 5,543,070, 3,901,741(cobalt, samarium, and gadolinium alloys), and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification. As will be apparent to thoseskilled in the art, especially upon studying the aforementioned patents,the saturation magnetization of thin films is often higher than thesaturation magnetization of bulk objects.

In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of the layer that containssuch material to the top surface of such layer that contains suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles.

Thus, e.g., one may make a thin film in accordance with the proceduredescribed at page 156 of Nature, Volume 407, Sep. 14, 2000, thatdescribes a multilayer thin film has a saturation magnetization of24,000 Gauss.

By the appropriate selection of nanomagnetic particles, and thethickness of the films deposited, one may obtain saturationmagnetizations of as high as at least about 36,000.

In the preferred embodiment depicted in FIG. 4, the nanomagneticparticles 24 are disposed within an insulating matrix so that any heatproduced by such particles will be slowly dispersed within such matrix.Such matrix, as indicated hereinabove, may be made from ceria, calciumoxide, silica, alumina. In general, the insulating material 42preferably has a thermal conductivity of less than about 20(caloriescentimeters/square centimeters-degree second)×10,000. See,e.g., page E-6 of the 63^(rd) Edition of the “Handbook of Chemistry andPhysics” (CRC Press, Inc., Boca Raton, Fla., 1982).

The nanomagnetic materials 24 typically comprise one or more of iron,cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g., typicalnanomagnetic materials include alloys of iron and nickel (permalloy),cobalt, niobium, and zirconium (CNZ), iron, boron, and nitrogen, cobalt,iron, boron, and silica, iron, cobalt, boron, and fluoride, and thelike. These and other materials are descried in a book by J. DouglasAdam et al. entitled “Handbook of Thin Film Devices” (Academic Press,San Diego, Calif., 2000). Chapter 5 of this book beginning at page 185,describes “magnetic films for planar inductive components and devices;”and Tables 5.1 and 5.2 in this chapter describe many magnetic materials.

FIG. 5 is a sectional view of the assembly 11 of FIG. 2. The device ofFIG. 5, and of the other Figures of this application, is preferablysubstantially flexible. As used in this specification, the term flexiblerefers to an assembly that can be bent to form a circle with a radius ofless than 2 centimeters without breaking. Put another way, the bendradius of the coated assembly 11 can be less than 2 centimeters.Reference may be had, e.g., to U.S. Pat. Nos. 4,705,353, 5,946,439,5,315,365, 4,641,917, 5,913,005, and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

As will be apparent, even when the magnetic insulating properties of theassembly of this invention are not 100 percent effective, the assemblystill prevents the rapid dissipation of heat to bodily tissue.

In another embodiment of the invention, there is provided a magneticallyshielded conductor assembly comprised of a conductor and a film ofnanomagnetic material disposed above said conductor. In this embodiment,the conductor has a resistivity at 20 degrees Centigrade of from about 1to about 2,000 micro ohm-centimeters and is comprised of a first surfaceexposed to electromagnetic radiation. In this embodiment, the film ofnanomagnetic material has a thickness of from about 100 nanometers toabout 10 micrometers and a mass density of at least about about 0.01gram per cubic centimeter, wherein the film of nanomagnetic material isdisposed above at least about 50 percent of said first surface exposedto electromagnetic radiation, and the film of nanomagnetic material hasa saturation magnetization of from about 1 to about 36,000 Gauss, acoercive force of from about 0.001 to about 5,000 Oersteds, a relativemagnetic permeability of from about 1 to about 2,000,000 and a magneticshielding factor of at least about 0.5. In this embodiment, thenanomagnetic material has an average particle size of less than about100 nanometers.

In the preferred embodiment of this invention, a film of nanomagnetic isdisposed above at least one surface of a conductor. Referring to FIG. 6,and in the schematic diagram depicted therein, a source ofelectromagnetic radiation 100 emits radiation 102 in the direction offilm 104. Film 104 is disposed above conductor 106, i.e., it is disposedbetween conductor 106 of the electromagnetic radiation 102.

The film 104 is adapted to reduce the magnetic field strength at point108 (which is disposed less than 1 centimeter above film 104) by atleast about 50 percent. Thus, if one were to measure the magnetic fieldstrength at point 108, and thereafter measure the magnetic fieldstrength at point 110 (which is disposed less than 1 centimeter belowfilm 104), the latter magnetic field strength would be no more thanabout 50 percent of the former magnetic field strength. Put another way,the film 104 has a magnetic shielding factor of at least about 0.5.

In one embodiment, the film 104 has a magnetic shielding factor of atleast about 0.9, i.e., the magnetic field strength at point 110 is nogreater than about 10 percent of the magnetic field strength at point108. Thus, e.g., the magnetic field strength at point 108 can be, e.g.,one Tesla, whereas the magnetic field strength at point 110 can be,e.g., 0.1 Tesla.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104 hasa saturation magnetization of form about 1 to about 36,000 Gauss. Thisproperty has been discussed elsewhere in this specification. In oneembodiment, the nanomagnetic material 103 a saturation magnetization offrom about 200 to about 26,000 Gauss.

The nanomagnetic material 103 in film 104 also has a coercive force offrom about 0.01 to about 5,000 Oersteds. The term coercive force refersto the magnetic field, H, which must be applied to a magnetic materialin a symmetrical, cyclicly magnetized fashion, to make the magneticinduction, B, vanish; this term often is referred to as magneticcoercive force. Reference may be had, e.g., to U.S. Pat. Nos. 4,061,824,6,257,512, 5,967,223, 4,939,610, 4,741,953, and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

In one embodiment, the nanomagnetic material 103 has a coercive force offrom about 0.01 to about 3,000 Oersteds. In yet another embodiment, thenanomagnetic material 103 has a coercive force of from about 0.1 toabout 10.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104preferably has a relative magnetic permeability of from about 1 to about500,000; in one embodiment, such material 103 has a relative magneticpermeability of from about 1.5 to about 260,000. As used in thisspecification, the term relative magnetic permeability is equal to B/H,and is also equal to the slope of a section of the magnetization curveof the film. Reference may be had, e.g., to page 4-28 of E.U. Condon etal.'s “Handbook of Physics” (McGraw-Hill Book Company, Inc., New York,1958).

Reference also may be had to page 1399 of Sybil P. Parker's “McGraw-HillDictionrary of Scientific and Technical Terms,” Fourth Edition (McGrawHill Book Company, New York, 1989). As is disclosed on this page 1399,permeability is “ . . . a factor, characteristic of a material, that isproportional to the magnetic induction produced in a material divided bythe magnetic field strength; it is a tensor when these quantities arenot parallel.

Reference also may be had, e.g., to U.S. Pat. Nos. 6,181,232, 5,581,224,5,506,559, 4,246,586, 6,390,443, and the like. The entire disclosure ofeach of these United States patents is hereby incorporated by referenceinto this specification.

In one embodiment, the nanomagnetic material 103 in film 104 has arelative magnetic permeability of from about 1.5 to about 2,000.

Referring again to FIG. 6, the nanomagnetic material 103 in film 104preferably has a mass density of at least about 0.01 grams per cubiccentimeter; in one embodiment, such mass density is at least about 1gram per cubic centimeter. As used in this specification, the term massdensity refers to the mass of a give substance per unit volume. See,e.g., page 510 of the aforementioned “McGraw-Hill Dictionary ofScientific and Technical Terms.” In one embodiment, the film 104 has amass density of at least about 3 grams per cubic centimeter. In anotherembodiment, the nanomagnetic material 103 has a mass density of at leastabout 4 grams per cubic centimeter.

In the embodiment depicted in FIG. 6, the film 104 is disposed above 100percent of the surfaces 112, 114, 116, and 118 of the conductor 106. Inthe embodiment depicted in FIG. 2, by comparison, the nanomagnetic filmis disposed around the conductor.

Yet another embodiment is depicted in FIG. 7. In the embodiment depictedin FIG. 7, the film 104 is not disposed in front of either surface 114,or 116, or 118 of the conductor 106. Inasmuch as radiation is notdirected towards these surfaces, this is possible.

What is essential, however, is that the film 104 be interposed betweenthe radiation 102 and surface 112. It is preferred that film 104 bedisposed above at least about 50 percent of surface 112. In oneembodiment, film 104 is disposed above at least about 90 percent ofsurface 112.

In the remainder of this specification, the use of film 104 with variousmedical devices will be discussed.

Many implanted medical devices have been developed to help medicalpractitioners treat a variety of medical conditions by introducing animplantable medical device, partly or completely, temporarily orpermanently, into the esophagus, trachea, colon, biliary tract, urinarytract, vascular system or other location within a human or veterinarypatient. For example, many treatments of the vascular system entail theintroduction of a device such as a guidewire, catheter, stent,arteriovenous shunt, angioplasty balloon, a cannula or the like. Otherexamples of implantable medical devices include, e.g., endoscopes,biopsy probes, wound drains, laparoscopic equipment, urethral inserts,and implants. Most such implantable medical devices are made in whole orin part of metal, and are not part of an electrical circuit.

When a patient with one of these implanted devices is subjected to highintensity magnetic fields, such as during magnetic resonance imaging(MRI), electrical currents are induced in the metallic portions of theimplanted devices. The electrical currents so induced often createsubstantial amounts of heat. The heat can cause extensive damage to thetissue surrounding the implantable medical device.

Furthermore, when a patient with one of these implanted devicesundergoes MRI, signal loss and disruption the diagnostic image oftenoccur as a result of the presence of a metallic object, which causes adisruption of the local magnetic field. This disruption of the localmagnetic field alters the relationship between position and frequency,which are crucial for proper image reconstruction. Therefore, patientswith implantable medical devices are generally advised not to undergoMRI procedures. In many cases, the presence of such a device is a strictcontraindication for MRI (See Shellock, F. G., Magnetic ResonanceProcedures: Health Effects and Safety, 2001 Edition, CRC Press, BocaRaton, Fla., and Food and Drug Administration, Magnetic ResonanceDiagnostic Device: Panel Recommendation and Report on Petitions for MRReclassification, Federal register, 1988, 53, 7575-7579). Anycontraindication such as this, whether a strict or relativecontraindication, is serious problem since it deprives the patient fromundergoing an MRI examination, or even using MRI to guide othertherapies, such as proper placement of diagnostic and/or therapeuticsdevices including angioplasty balloons, RF ablation catheters fortreatment of cardiac arrythmias, sensors to assess the status ofpharmacological treatment of tumors, or verification of proper placementof other permanently implanted medical devices. The rapidly growingcapabilities and use of MRI in these and other areas prevent anincreasingly large group of patients from benefiting from this powerfuldiagnostic and intra-operative tool.

The use of implantable medical devices is well known in the prior art.Thus, e.g., U.S. Pat. No. 4,180,600 discloses and claims an implantablemedical device comprising a shielded conductor wire consisting of aconductive copper core and a magnetically soft alloy metallic sheathmetallurgically secured to the conductive core, wherein the sheathconsists essentially of from 2 to 5 weight percent of molybdenum, fromabout 15 to about 23 weight percent of iron, and from about 75 to about85 weight percent of nickel. Although the device of this patent doesprovide magnetic shielding, it still creates heat when it interacts withstrong magnetic fields, and it can still disrupt and distort magneticresonance images.

Thus, e.g., U.S. Pat. No. 5,817,017 discloses and claims an implantablemedical device having enhanced magnetic image visibility. The magneticimages are produced by known magnetic imaging techniques, such as MRI.The invention disclosed in the '017 patent is useful for modifyingconventional catheters, stents, guide wires and other implantabledevices, as well as interventional devices, such as for suturing,biopsy, which devices may be temporarily inserted into the body lumen ortissue; and it is also useful for permanently implantable devices.

As is disclosed in the '017 patent, paramagnetic ionic particles arefixedly incorporated and dispersed in selective portions of animplantable medical device such as, e.g., a catheter. When the cathetercoated with paramagnetic ionic particles is inserted into a patientundergoing magnetic resonance imaging, the image signal produced by thecatheter is of higher intensity. However, paramagnetic implants,although less susceptible to magnetization than ferromagnetic implants,can produce image artifacts in the presence of a strong magnetic field,such as that of a magnetic resonant imaging coil, due to eddy currentsgenerated in the implants by time-varying electromagnetic fields that,in turn, disrupt the local magnetic field and disrupt the image.

Any electrically conductive material, even a non-metallic material, andeven if not in an electrical circuit, will develop eddy currents andthus produce electrical potential and thermal heating in the presence ofa time-varying electromagnetic field or a radio frequency field.

Thus, there is a need to provide an implantable medical device, which isshielded from strong electromagnetic fields, which does not create largeamounts of heat in the presence of such fields, and which does notproduce image artifacts when subjected to such fields. It is one objectof the present invention to provide such a device.

FIGS. 8A, 8B, 8C, and 8D are schematic sectional views of a substrate201, which is preferably a part of an implantable medical device.

Referring to FIG. 8A, it will be seen that substrate 201 is coated withnanomagnetic particles 202 on the exterior surface 203 of the substrate.

Referring to FIG. 8B, and in the embodiment depicted therein, thesubstrate 201 is coated with nanomagnetic particulate 202 on both theexterior surface 203 and the interior surface 204.

Referring to FIG. 8C, and in the preferred embodiment depicted therein,a layer of insulating material 205 separates substrate 201 and the layerof nanomagnetic coating 202.

Referring to FIG. 8D, it will be seen that one or more layers ofinsulating material 205 separate the inside and outside surfaces ofsubstrate 201 from respective layers of nanomagnetic coating 202.

FIG. 9 is a schematic sectional view of a substrate 301 which is part ofan implantable medical device (not shown). Referring to FIG. 9, and inthe embodiment depicted therein, it will be seen that substrate 301 iscoated with nanomagnetic material 302, which may differ fromnanomagnetic material 202.

In one embodiment, the substrate 301 is in the shape of a cylinder, suchas an enclosure for a medical catheter, stent, guide wire, and the like.In one aspect of this embodiment, the cylindrical substrate 301 enclosesa helical member 303, which is also coated with nanomagnetic particulatematerial 302.

In another embodiment (not shown), the cylindrical substrate 301depicted in FIG. 9 is coated with multiple layers of nanomagneticmaterials. In one aspect of this embodiment, the multiple layers ofnanomagnetic particulate are insulated from each other. In anotheraspect of this embodiment, each of such multiple layers is comprised ofnanomagnetic particles of different sizes and/or densities and/orchemical densities. In one aspect of this embodiment, not shown, each ofsuch multiple layers may have different thickness. In another aspect ofthis embodiment, the frequency response and degree of shielding of eachsuch layer differ from that of one or more of the other such layers.

FIG. 10 is a flow diagram of a preferred process of the invention. InFIG. 2, reference is made to one or more conductors as being thesubstrate(s); it is to be understood, however, that other substrate(s)material(s) and/or configurations also may be used.

In the first step of this process depicted in FIG. 10, step 240, thesubstrate 201 (see FIG. 8A) is coated with electrical insulativematerial. Suitable insulative materials include nano-sized silicondioxide, aluminum oxide, cerium oxide, yttrium-stabilized zirconium,silicon carbide, silicon nitride, aluminum nitride, and the like. Ingeneral, these nano-sized particles will have a particle distributionsuch that at least 90 weight percent of the particles have a dimensionin the range of from about 10 to about 100 nanometers.

The coated substrate 201 may be prepared by conventional means such as,e.g., the process described in U.S. Pat. No. 5,540,959, the entiredisclosure of which is incorporated by reference into thisspecification. This patent describes and claims a process for preparinga coated substrate, comprising the steps of: (a) creating mist particlesfrom a liquid, wherein: 1. said liquid is selected from the groupconsisting of a solution, a slurry, and mixtures thereof, 2. said liquidis comprised of solvent and from 0.1 to 75 grams of solid material perliter of solvent, 3. at least 95 volume percent of said mist particleshave a maximum dimension less than100 microns, and 4. said mistparticles are created from said first liquid at a rate of from 0.1 to 30milliliters of liquid per minute; (b) contacting said mist particleswith a carrier gas at a pressure of from 761 to 810 millimeters ofmercury; (c) thereafter contacting said mist particles with alternatingcurrent radio frequency energy with a frequency of at least 1 megahertzand a power of at least 3 kilowatts while heating said mist to atemperature of at least 100 degree centigrade, thereby producing aheated vapor; (d) depositing said heated vapor onto a substrate, therebyproducing a coated substrate; and (e) subjecting said coated substrateto a temperature of from about 450 to about 1,400 degree centigrade forat least 10 minutes.

By way of further illustration, one may coat substrate 201 by means ofthe process disclosed in a text by D. Satas on “Coatings TechnologyHandbook” (Marcel Dekker, Inc., New York, N.Y., 1991). As is disclosedin such text, one may use cathodic arc plasma deposition (see pages 229et seq.), chemical vapor deposition (see pages 257 et seq.), sol-gelcoatings (see pages 655 et seq.), and the like.

Referring again to FIGS. 8C and 8D, and by way of illustration and notlimitation, these Figures are sectional views of the coated substrate201. It will be seen that, in the embodiments depicted, insulatingmaterial 205 separates the substrate and the layer of nanomagneticmaterial 202. In order to obtain the structure depicted in FIGS. 8C and8D, one may first coat the substrate with insulating material 205, andthen apply a coat of nanomagnetic material 202 on top of the insulatingmaterial 205; see, e.g., step 248 of FIG. 10.

The insulating material 205 that is disposed between substrate 201 andthe layer of nanomagnetic coating 202 preferably has an electricalresistivity of from about 1,000,000,000 to about 10,000,000,000,000ohm-centimeter.

After the insulating material 205 has been deposited, and in onepreferred embodiment, the coated substrate is heat-treated in step 250of FIG. 10. The heat treatment often is preferably used in conjunctionwith coating processes in which heat is required to bond the insulativematerial to the substrate 201.

The heat-treatment step 250 may be conducted after the deposition of theinsulating material 205, or it may be conducted simultaneouslytherewith. In either event, and when it is used, it is preferred to heatthe coated substrate 201 to a temperature of from about 200 to about 600degree Centigrade for about 1 minute to about 10 minutes.

Referring again to FIG. 10, and in step 252 of the process, after thecoated substrate 201 has been subjected to heat treatment step 250, thesubstrate is allowed to cool to a temperature of from about 30 to about100 degree Centigrade over a period of time of from about 3 to about 15minutes.

One need not invariably heat-treat and/or cool. Thus, referring to FIG.10, one may immediately coat nanomagnetic particulate onto the coatedsubstrate in step 254, after step 248 and/or after step 250 and/or afterstep 252.

In step 254, nanomagnetic material(s) are coated onto the previouslycoated substrate 201. This is best shown in FIGS. 8C and 8D, wherein thenanomagnetic materials are identified as 202.

Nanomagnetic material is magnetic material which has an average particlesize less than 100 nanometers and, preferably, in the range of fromabout 2 to about 50 nanometers. Reference may be had, e.g., to U.S. Pat.Nos. 5,889,091 (Rotationally Free Nanomagnetic Material), 5,714,136,5,667,924, and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

The nanomagnetic material may be, e.g., nano-sized ferrites such as,e.g., the nanomagnetic ferrites disclosed in U.S. Pat. No. 5,213,851,the entire disclosure of which is hereby incorporated by reference intothis specification. This patent discloses and claim a process forcoating a layer of ferrite material with a thickness of from about 0.1to about 500 microns onto a substrate at a deposition rate of from about0.01 to about 10 microns per minute per 35 square centimeters ofsubstrate surface, comprising the steps of: (a) providing a solutioncomprised of a first compound and a second compound, wherein said firstcompound is an iron compound and said second compound is selected fromthe group consisting of compound of nickel, zinc, magnesium, strontium,barium, manganese, lithium, lanthanum, yttrium, scandium, samarium,europium, terbium, dysprosium, holmium, erbium, ytterbium, lutetium,cerium, praseodymium, thulium, neodymium, gadolinium, aluminum, iridium,lead, chromium, gallium, indium, cobalt, titanium, and mixtures thereof,and wherein said solution is comprised of from about 0.01 to about 1kilogram of a mixture consisting essentially of said compounds per literof said solution; (b) subjecting said solution to ultrasonic sound wavesat a frequency in excess of 20 kilohertz, and to an atmospheric pressureof at least about 600 millimeters of mercury, thereby causing saidsolution to form into an aerosol; (c) providing a radio frequency plasmareactor comprised of a top section, a bottom section, and a radiofrequency coil; (d) generating a hot plasma gas within said radiofrequency plasma reactor, thereby producing a plasma region; (e)providing a flame region disposed above said top section of said radiofrequency plasma reactor; (f) contacting said aerosol with said hotplasma gas within said plasma reactor while subjecting said aerosol toan atmospheric pressure of at least 600 millimeters of mercury, and to aradio frequency alternating current at a frequency of from about 100kilohertz to about 30 megahertz, thereby forming a vapor; (g) providinga substrate disposed above said flame region; and (h) contacting saidvapor with said substrate, thereby forming said layer of ferritematerial.

By way of further illustration, one may use the techniques described inan article by M. De Marco, X. W. Wang, et at. on “Mossbauer andMagnetization Studies of Nickel Ferrites”, published in the Journal ofApplied Physics 73(10), May 15, 1993, at pages 6287-6289.

In general, the thickness of the layer of nanomagnetic materialdeposited onto the coated substrate 201 is from about 100 nanometers toabout 10 micrometers and, more preferably, from about 0.1 to 3 microns.

Referring again to FIG. 10, after the nanomagnetic material is coated instep 254, the coated substrate may be heat-treated in step 256. In thisoptional step 256, it is preferred to subject the coated substrate 201to a temperature of from about 200 to about 600 degree Centigrade forfrom about 1 to about 10 minutes.

In one embodiment (not shown) additional insulating layers may be coatedonto the substrate 201, by one or more of the processes disclosedhereinabove; see, e.g., optional step 258 of FIG. 10.

Without wishing to be bound to any particular theory, the applicantsbelieve that the nanomagnetic particles 202 trap and pin magnetic linesof flux impinging on substrate 201, while at the same time minimizing oreliminating the flow of electrical currents through the coating and/orsubstrate.

In order to function optimally, the nanomagnetic material(s) 202preferably have a specified magnetization. As is know to those skilledin the art, magnetization is the magnetic moment per unit volume of asubstance. Reference may be had, e.g., to U.S. Pat. Nos. 4,169,998,4,168,481, 4,166,263, 5,260,132, 4,778,714, and the like. The entiredisclosure of each of these United States patents is hereby incorporatedby reference into this specification.

Referring again to FIGS. 8A, 8B, 8C, and 8D, the layer of nanomagneticparticles 202 preferably has a saturation magnetization, at 25 degreeCentigrade, of from about 1 to about 36,000 Gauss. and preferably fromabout 1 to about 26,000 Gauss. In one embodiment, the saturationmagnetization at room temperature of the nanomagnetic particles is fromabout 500 to about 10,000 Gauss. For a discussion of the saturationmagnetization of various materials, reference may be had, e.g., to U.S.Pat. Nos. 4,705,613, 4,631,613, 5,543,070, 4,901,741 (cobalt, samarium,and gadolinium alloys), and the like. The entire disclosure of each ofthese United States patents is hereby incorporated by reference intothis specification. As will be apparent to those skilled in the art,especially upon studying the aforementioned patents, the saturationmagnetization of thin films is often higher than the saturationmagnetization of bulk objects.

In one embodiment, it is preferred to utilize a thin film with athickness of less than about 2 microns and a saturation magnetization inexcess of 20,000 Gauss. The thickness of the layer of nanomagneticmaterial is measured from the bottom surface of such layer that containssuch material to the top surface of such layer that contain suchmaterial; and such bottom surface and/or such top surface may becontiguous with other layers of material (such as insulating material)that do not contain nanomagnetic particles. Thus, e.g., one may make athin film in accordance with the procedure described at page 156 ofNature, Volume 407, Sep. 14, 2000, that describes a multiplayer thinfilm that has a saturation magnetization of 24,000 Gauss.

By the appropriate selection of nanomagnetic particles, and thethickness of the film deposited, one may obtain saturationmagnetizations of as high as at least about 36,000 Gauss.

In the preferred embodiment depicted in FIG. 8A, the nanomagneticmaterial 202 may be disposed within an insulating matrix (not shown) sothat any heat produced by such particles will be slowly dispersed withinsuch matrix. Such matrix, as indicated hereinabove, may be made fromceria, calcium oxide, silica, alumina, and the like. In general, theinsulating material 202 preferably has a thermal conductivity of lessthan about 20 (calories centimeters/square centimeters-degreesecond)×10,000. See, e.g., page E-6 of the 63^(rd). Edition of the“Handbook of Chemistry and Physics” (CRC Press, Inc. Boca Raton, Fla.,1982).

The nanomagnetic material 202 typically comprises one or more of iron,cobalt, nickel, gadolinium, and samarium atoms. Thus, e.g., typicalnanomagnetic materials include alloys of iron, and nickel (permalloy),cobalt, niobium and zirconium (CNZ), iron, boron, and nitrogen, cobalt,iron, boron and silica, iron, cobalt, boron, and fluoride, and the like.These and other materials are described in a book by J. Douglass Adam etal. entitled “Handbook of Thin Film Devices” (Academic Press, San Diego,Calif., 2000). Chapter 5 of this book beginning at page 185 describes“magnetic films for planar inductive components and devices;” and Tables5.1.and 5.2 in this chapter describes many magnetic materials.

Some of the devices described in this application are substantiallyflexible. As used in this specification, the term flexible refers to anassembly that can be bent to form a circle with a radius of less than 2centimeters without braking. Put another way, the bend radius of thecoated assembly can be less than 2 centimeters. Reference may be had,e.g., to U.S. Pat. Nos. 4,705,353, 5,946,439, 5,315,365, 4,641,917,5,913,005, and the like. The entire disclosure of each of these UnitedStates patents is hereby incorporated by reference into thisspecification.

As will be apparent, even when the magnetic insulating properties of theassembly of this invention are not absolutely effective, the assemblystill reduces the amount of electromagnetic energy that is transferredto the coated substrate, prevents the rapid dissipation of heat tobodily tissue, and minimization of disruption to the magnetic resonanceimage.

FIG. 11 is schematic sectional view of a substrate 401, which is part ofan implantable medical device (not shown). Referring to FIG. 11, and inthe preferred embodiment depicted therein, it will be seen thatsubstrate 401 is coated with a layer 404 of nanomagnetic material(s).The layer 404, in the embodiment depicted, is comprised of nanomagneticparticulate 405 and nanomagnetic particulate 406. Each of thenanomagnetic particulate 405 and nanomagnetic particulate 406 preferablyhas an elongated shape, with a length that is greater than its diameter.In one aspect of this embodiment, nanomagnetic particles 405 have adifferent size than nanomagnetic particles 406. In another aspect ofthis embodiment, nanomagnetic particles 405 have different magneticproperties than nanomagnetic particles 406. Referring again to FIG. 11,and in the preferred embodiment depicted therein, nanomagneticparticulate material 405 and nanomagnetic particulate material 406 aredesigned to respond to an static or time-varying electromagnetic fieldsor effects in a manner similar to that of liquid crystal display (LCD)materials. More specifically, these nanomagnetic particulate materials405 and nanomagnetic particulate materials 406 are designed to shiftalignment and to effect switching from a magnetic shielding orientationto a non-magnetic shielding orientation. As will be apparent, themagnetic shield provided by layer 404, can be turned “ON” and “OFF” upondemand. In yet another embodiment (not shown), the magnetic shield isturned on when heating of the shielded object is detected.

FIG. 12 is a schematic sectional view of substrate 501, which is part ofan implantable medical device (not shown). Referring to FIG. 12, and tothe embodiment depicted therein, it will be seen that substrate 501 iscoated with nanomagnetic particulate material 502 which may differ fromparticulate material 202 and/or particulate material 302. In theembodiment depicted in FIG. 12, the substrate 501 may be a cylinder,such as an enclosure for a catheter, medical stent, guide wire, and thelike. The assembly depicted in FIG. 12 includes a channel 508 located onthe periphery of the medical device. An actively circulating,heat-dissipating fluid (not shown) can be pumped into channel 508through port 507, and exit channel 508 through port 509. Theheat-dissipation fluid (not shown) will draw heat to another region ofthe device, including regions located outside of the body where the heatcan be dissipated at a faster rate. In the embodiment depicted, theheat-dissipating flow flows internally to the layer of nanomagneticparticles 502.

In another embodiment, not shown, the heat dissipating fluid flowsexternally to the layer of nanomagnetic particulate material 502.

In another embodiment (not shown), one or more additional polymer layers(not shown) are coated on top of the layer of nomagnetic particulate502. In one aspect of this embodiment, a high thermal conductivitypolymer layer is coated immediately over the layer of nanomagneticparticulate 502; and a low thermal conductivity polymer layer is coatedover the high thermal conductivity polymer layer. It is preferred thatneither the high thermal conductivity polymer layer nor the low thermalconductivity polymer layer be electrically or magnetically conductive.In the event of the occurrence of “hot spots” on the surface of themedical device, heat from the localized “hot spots” will be conductedalong the entire length of the device before moving radially outwardthrough the insulating outer layer. Thus, heat is distributed moreuniformly.

Many different devices advantageously incorporate the nanomagnetic filmof this invention. In the following section of the specification,various additional devices that incorporate the such film are described.

The disclosure in the following section of the specification relatesgenerally to an implantable medical device that is immune or hardened toelectromagnetic insult or interference. More particularly, the inventionis directed to implantable medical devices that are not part of anelectrical circuit, and that utilize shielding to harden or make thesedevices immune from electromagnetic insult (i.e. minimize or eliminatethe amount of electromagnetic energy transferred to the device), namelymagnetic resonance imaging (MRI) insult

Magnetic resonance imaging (MRI) has been developed as an imagingtechnique to obtain images of anatomical features of human patients aswell as some aspects of the functional activities of biological tissue;reference may be had, e.g., to John D. Enderle's “Introduction toBiomedical Engineering”, Academic Press, San Diego, Calif., 2000 and, inparticular, pages 783-841 thereof. Reference may also be had to JosephD. Bronzino's “The Biomedical Engineering Handbook”, CRC Press, BocaRaton, Fla., 1995, and in particular pages 1006-1045 thereof. Theseimages have medical diagnostic value in determining the state of thehealth of the tissue examined.

In an MRI process, a patient is typically aligned to place the portionof the patient's anatomy to be examined in the imaging volume of the MRIapparatus. Such a MRI apparatus typically comprises a primary magnet forsupplying a constant magnetic field, Bo, which is typically of fromabout 0.5 to about 8.0 Tesla, and by convention, is along the z-axis andis substantially homogenous over the imaging volume, and secondarymagnets that can provide magnetic field gradients along each of thethree principal Cartesian axis in space (generally x, y, and z or x1,x2, and x3, respectively). A magnetic field gradient refers to thevariation of the field along the direction parallel to Bo with respectto each of the three principal Cartesian Axis. The apparatus alsocomprises one or more radio frequency (RF) coils, which provideexcitation for and detection of the MRI signal. The RF excitation signalis an electromagnetic wave with an electrical field E and magnetic fieldB1, and is typically transmitted at frequencies of 3-100 megahertz.

The use of the MRI process with patients who have implanted medicalassist devices, such as guide wires, catheters, or stents, oftenpresents problems. These implantable devices are sensitive to a varietyof forms of electromagnetic interference (EMI), because theaforementioned devices contain metallic parts that are sensitive to EMI.The above-mentioned devices may also contain sensing and logic andcontrol systems that respond to low-level electrical signals emanatingfrom the monitored tissue region of the patient. Since these implanteddevices are responsive to changes in local electromagnetic fields, theimplanted devices are vulnerable to sources of electromagnetic noise.The implanted devices interact with the time-varying radio-frequency(RF) magnetic field (B1), which are emitted during the MRI procedure.This interaction can result in damage to the implantable device, or itcan result in heating of the device, which in turn can harm the patientor physician using the device. This interaction can also result indegradation of the quality of the image obtained by the MRI process.

Signal loss and disruption of a magnetic resonance image can be causedby disruption of the local magnetic field, which perturbs therelationship between position and image, which are crucial for properimage reconstruction. More specifically, the spatial encoding of the MRIsignal provided by the linear magnetic field can be disrupted, makingimage reconstruction difficult or impossible. The relative amount ofartifact seen on an MR image due to signal disruption is dependent uponsuch factors as the magnetic susceptibility of the materials used in theimplantable medical device, as well as the shape, orientation, andposition of the medical device within the body of the patient, which isvery often difficult to control.

All non-permanently magnetized materials have non-zero magneticsusceptibilities and are to some extent magnetic. Materials withpositive magnetic susceptibilities less than approximately 0.01 arereferred to as paramagnetic and are not overly responsive to an appliedmagnetic field. They are often considered non-magnetic. Materials withmagnetic susceptibilities greater than 0.01 are referred to asferromagnetic. These materials can respond very strongly to an appliedmagnetic field and are also referred as soft magnets as their propertiesdo not manifest until exposed to an external magnetic field.

Paramagnetic materials (e.g. titanium), are frequently used toencapsulate and shield and protect implantable medical devices due totheir low magnetic susceptibilities. These enclosures operate bydeflecting electromagnetic fields. However, although paramagneticmaterials are less susceptible to magnetization than ferromagneticmaterials, they can also produce image artifacts due to eddy currentsgenerated in the implanted medical device by externally applied magneticfields, such as the radio frequency fields used in the MRI procedures.These eddy currents produce localized magnetic fields, which disrupt anddistort the magnetic resonance image. Furthermore, the implanted medicaldevice shape, orientation, and position within the body make itdifficult to control image distortion due to eddy currents induced bythe RF fields during MRI procedures. Also, since the paramagneticmaterials are electrically conductive, the eddy currents produced inthem can result in ohmic heating and injury to the patient. The voltagesinduced in the paramagnetic materials can also damage the medicaldevice, adversely interact with the operation of the device. Typicaladverse effects can include improper stimulation of internal tissues andorgans, damage to the medical device (melting of implantable cathetersawhile in the MR coil have been reported in the literature), and/orinjury to the patient.

Thus, it is desirable to provide protection against electromagneticinterference, and to also provide fail-safe protection against radiationproduced by magnetic-resonance imaging procedures. Moreover, it isdesirable to provide devices that prevent the possible damage that canbe done at the tissue interface due to induced electrical signals anddue to thermal tissue damage. Furthermore, it is desirable to providedevices that do not interact with RF fields which are emitted duringmagnetic-resonance imaging procedures and which result in degradation ofthe quality of the images obtained during the MRI process.

In one embodiment, there is provided a coating of nanomagnetic particlesthat consists of a mixture of aluminum oxide (AlO3), iron, and otherparticles that have the ability to deflect electromagnetic fields whileremaining electrically non-conductive. Preferably the particle size insuch a coating is approximately 10 nanometers. Preferably the particlepacking density is relatively low so as to minimize electricalconductivity. Such a coating when placed on a fully or partiallymetallic object (such as a guide wire, catheter, stent, and the like) iscapable of deflecting electromagnetic fields, thereby protectingsensitive internal components, while also preventing the formation ofeddy currents in the metallic object or coating. The absence of eddycurrents in a metallic medical device provides several advantages, towit: (1) reduction or elimination of heating, (2) reduction orelimination of electrical voltages which can damage the device and/orinappropriately stimulate internal tissues and organs, and (3) reductionor elimination of disruption and distortion of a magnetic-resonanceimage.

FIG. 13 is a schematic view of a catheter assembly 600 similar to theassembly depicted in FIG. 2 of U.S. Pat. No. 3,995,623; the entiredisclosure of such patent is hereby incorporated by reference into thisspecification. Referring to FIG. 6 of such patent, it will be seen thatcatheter tube 625 contains multiple lumens 603, 611, 613, and 615, whichcan be used for various functions such as inflating balloons, enablingelectrical conductors to communicate with the distal end of thecatheter, etc. While four lumens are shown, it is to be understood thatthis invention applies to a catheter with any number of lumens.

The similar catheter disclosed and claimed in U.S. Pat. No. 3,995,623may be shielded by coating it in whole or in part with a coating ofnanomagnetic particulate, in any of the following manners:

In FIG. 13A, a nanomagnetic material 650 is applied to either theinterior wall 650 a or exterior wall 650 b of lumens 603, 611, 613, and615, or imbibed 650 c into the walls of these lumens within catheter625, or any combination of these locations.

In FIG. 13B, a nanomagnetic material 650 is applied to the interiorwalls 650 d of multiple lumens within a single catheter 625 or thecommon exterior wall 650 b or imbibed 650 c into the common wall.

In FIG. 13C, a nanomagnetic material 650 is applied to the mesh-likematerial 636 used within the wall of catheter 625 to give it desiredmechanical properties.

In another embodiment (not shown) a sheath coated with nanomagneticmaterial on its internal surface, exterior surface, or imbibed into thewall of sheath is placed over the catheter to shield it fromelectromagnetic interference. In this manner, existing catheters can bemade MRI safe and compatible. The modified catheter assembly thusproduced is resistant to electromagnetic radiation.

FIGS. 14A through 14G are schematic views of a catheter assemblyconsisting of multiple concentric elements. While two elements areshown; 720 and 722, it is to be understood that any number ofover-lapping elements may be used, either concentrically or planarlypositioned with respect to each other.

Referring to FIGS. 14A-14G, it will be seen that catheter assembly 700comprises an elongated tubular construction having a single, central oraxial lumen 710. The exterior catheter body 722 and concentricallypositioned internal catheter body 720 with internal lumen 712 arepreferably flexible, i.e., bendable, but substantially non-compressiblealong its length. The catheter bodies 720 and 722 may be made of anysuitable material. A presently preferred construction comprises an outerwall 722 and inner wall 720 made of a polyurethane, silicone, or nylon.The outer wall 722 preferably comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter assembly 700 so that, when a control handle, not shown, isrotated, the tip sectionally of the catheter will rotate incorresponding manner. The catheter assembly 700 may be shielded bycoating it in whole or in part with a coating of nanomagneticparticulate, in any one or more of the following manners:

Referring to FIG. 14A, a nanomagnetic material may be coated on theoutside surface of the inner concentrically positioned catheter body720.

Referring to FIG. 14B, a nanomagnetic material may be coated on theinside surface of the inner concentrically positioned catheter body 720.

Referring to FIG. 14C, a nanomagnetic material may be imbibed into thewalls of the inner concentrically positioned catheter body 720 andexternally positioned catheter body 722. Although not shown, ananomagnetic material may be imbibed solely into either innerconcentrically positioned catheter body 720 or externally positionedcatheter body 722.

Referring to FIG. 14D, a nanomagnetic material may be coated onto theexterior wall of the inner concentrically positioned catheter body 720and external catheter body 722.

Referring to FIG. 14E, a nanomagnetic material may be coated onto theinterior wall of the inner concentrically positioned catheter body 720and externally wall of externally positioned catheter body 722.

Referring to FIG. 14F, a nanomagnetic material may be coated on theoutside surface of the externally positioned catheter body 722.

Referring to FIG. 14G, a nanomagnetic material may be coated onto theexterior surface of an internally positioned solid element 727.

By way of further illustration, one may apply nanomagnetic particulatematerial to one or more of the catheter assemblies disclosed and claimedin U.S. Pat. Nos. 5,178,803, 5,041,083, 6,283,959, 6,270,477, 6,258,080,6,248,092, 6,238,408, 6,208,881, 6,190,379, 6,171,295, 6,117,064,6,019,736, 6,017,338, 5,964,757, 5,853,394, and 6,235,024, the entiredisclosure of which is hereby incorporated by reference into thisspecification. The catheters assemblies disclosed and claimed in theabove-mentioned United States patents may be shielded by coating them inwhole or in part with a coating of nanomagmetic particulate. Themodified catheter assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 15A, 15B, and 15C are schematic views of a guide wire assembly 800for insertion into vascular vessel (not shown), and it is similar to theassembly depicted in U.S. Pat. No. 5,460,187, the entire disclosure ofsuch patent is incorporated by reference into this specification.Referring to FIG. 15A, a coiled guide wire 810 is formed of a proximalsection (not shown) and central support wire 820 which terminates inhemispherical shaped tip 815. The proximal end has a retaining device(not shown) enables the person operating the guide wire to turn anorient the guide wire within the vascular conduit.

The guide wire assembly may be shielded by coating it in whole or inpart with a coating of nanomagnetic particulate, in any of the followingmanners:

Referring to FIG. 15A; the nanomagnetic material 650 is coated on theexterior surface of the coiled guidewire 810.

Referring to FIG. 15B; the nanomagnetic material 650 is coated on theexterior surface of the central support wire 820.

Referring to FIG. 15C; the nanomagnetic material 650 is coated on allguide wire assembly components including coiled guide wire 810, tip 815,and central support wire 820.

The modified guide wire assembly thus produced is resistant toelectromagnetic radiation.

By way of further illustration, one may coat with nanomagneticparticulate matter the guide wire assemblies disclosed and claimed inU.S. Pat. Nos.: 5,211,183, 6,168,604, 6,093,157, 6,019,737, 6,001,068,5,938,623, 5,797,857, 5,588,443, and 5,452,726 the entire disclosure ofwhich is hereby incorporated by reference into this specification. Themodified guide wire assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 16A and 16B are schematic views of a medical stent assembly 900similar to the assembly depicted in FIG. 15 of U.S. Pat. No. 5,443,496;the entire disclosure of such patent is hereby incorporated by referenceinto this specification.

Referring to FIG. 16A, a self-expanding stent 900 comprising joinedmetal stent elements 962 are shown. The stent 960 also comprises aflexible film 964. The flexible film 964 can be applied as a sheath tothe metal stent elements 962 after which the stent 960 can becompressed, attached to a catheter, and delivered through a body lumento a desired location. Once in the desired location, the stent 960 canbe released from the catheter and expanded into contact with the bodylumen, where it can conform to the curvature of the body lumen. Theflexible film 964 is able to form folds, which allow the stent elementsto readily adapt to the curvature of the body lumen. The medical stentassembly disclosed and claimed in U.S. Pat. No. 5,443,496 may beshielded by coating it in whole or in part with a nanomagnetic coatingin any of the following manners:

Referring to FIG. 16A, flexible film 964 may be coated with ananomagnetic coating on its inside or outside surfaces, or within thefilm itself.

In one embodiment, a stent (not shown) is coated with a nanomagneticmaterial.

It is to be understood that any one of the above embodiments may be usedindependently or in conjunction with one another within a single device.

In yet another embodiment (not shown), a sheath (not shown), coated orimbibed with a nanomagnetic material is placed over the stent,particularly the flexible film 964, to shield it from electromagneticinterference. In this manner, existing stents can be made MRI safe andcompatible.

By way of illustration and not limitation, one may coat one or more ofthe medical stent assemblies disclosed and claimed in U.S. Pat. Nos.:6,315,794, 6,190,404, 5,968,091, 4,969,458, 6,342,068, 6,312,460,6,309,412, and 6,305,436, the entire disclosure of each of which ishereby incorporated by reference into this specification. The medicalstent assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagnetic particulate, as described above. The modifiedmedical stent assemblies thus produced are resistant to electromagneticradiation.

FIG. 17 is a schematic view of a biopsy probe assembly 1000 similar tothe assembly depicted in FIG. 1 of U.S. Pat. No. 5,005,585 the entiredisclosure of such patent is hereby incorporated by reference into thisspecification.

Referring to FIG. 17, the biopsy probe assembly is composed of threeseparate components, a hollow tubular cannula or needle 1001, a solidintraluminar rod-like stylus 1002, and a clearing rod or probe (notshown).

The components of the assembly are preferably formed of an alloy, suchas stainless steel, which is corrosion resistant and non-toxic. Cannula1001 has a proximal end (not shown) and a distal end 1005 that is cut atan acute angle with respect to the longitudinal axis of the cannula andprovides an annular cutting edge.

By way of further illustration, biopsy probe assemblies are disclosedand claimed in U.S. Pat. Nos.: 4,671,292, 5,437,283, 5,494,039,5,398,690, and 5,335,663, the entire disclosure of each of which ishereby incorporated by reference into this specification. The biopsyprobe assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagmetic particulate, in any of the following manners:Cannula 1001 may be coated, intraluminar stylus 1002 may be coated,and/or the clearing rod may be coated.

In one variation on this design (not shown), a biocompatible sheath isplaced over the coated cannula 1001 to protect the nanomagnetic coatingfrom abrasion and from contacting body fluids.

In one variation on this design (not shown), the biocompatible sheathhas on its interior surface or within its walls a nanomagnetic coating.

In yet another embodiment (not shown), a sheath (not shown), coated orimbibed with a nanomagnetic material is placed over the biopsy probe, toshield it from electromagnetic interference. In this manner, existingstents can be made MRI safe and compatible.

The modified biopsy probe assemblies thus produced are resistant toelectromagnetic radiation.

FIGS. 18A and 18B are schematic views of a flexible tube endoscopeassembly 1180 similar to the assembly depicted in FIG. 1 of U.S. Pat.No. 5,058,567 the entire disclosure of such patent is herebyincorporated by reference into this specification.

MRI is increasingly being used to guide the placement of endoscopes,which are very good at examining tissues close up, but generally cannotaccurately determine where the tissues being examined are located withinthe body.

Referring to FIG. 18A, the endoscope 1100 employs a flexible tube 1110with a distally positioned objective lens 1120. Flexible tube 1110 ispreferably formed in such manner that the outer side of a spiral tube isclosely covered with a braided-wire tube (not shown) formed by weavingfine metal wires into a braid. The spiral tube is formed using aprecipitation hardening alloy material, for example, beryllium bronze(copper-beryllium alloy).

By way of further illustration, endoscope tube assemblies are disclosedand claimed in U.S. Pat. Nos.: 4,868,015, 4,646,723, 3,739,770,4,327,711, and 3,946,727, the entire disclosure of each of which ishereby incorporated by reference into this specification. The endoscopetube assemblies disclosed and claimed in the above-mentioned UnitedStates patents may be shielded by coating them in whole or in part witha coating of nanomagmetic particulate, in any of the following manners:

Referring to FIG. 18A; sheath 1180 is a sheath coated with nanomagneticmaterial on its inside surface 650 a, exterior surface 650 b, or imbibedinto its structure 650 c; and such sheath is placed over the endoscope,particularly the flexible tube 1110, to shield it from electromagneticinterference.

In yet another embodiment (not shown), flexible tube 1110 is coated withnanomagnetic materials on its internal surface, or imbibed withnanomagnetic materials within its wall.

In another embodiment (not shown), the braided-wire element withinflexible tube 1110 is coated with a nanomagnetic material.

In this manner, existing endoscopes can be made MRI safe and compatible.The modified endoscope tube assemblies thus produced are resistant toelectromagnetic radiation.

It is to be understood that the aforementioned description isillustrative only and that changes can be made in the apparatus, in theingredients and their proportions, and in the sequence of combinationand process steps, as well as in other aspects of the inventiondiscussed herein, without departing from the scope of the invention asdefined in the following claims.

1. A magnetically shielded conductor assembly comprised of a conductorand a film of nanomagnetic material disposed above said conductor,wherein: (a) said conductor has a resistivity at 20 degrees Centigradeof from about 1 to about 2,000 micro ohm-centimeters and is comprised ofa first surface exposed to electromagnetic radiation; (b) said film ofnanomagnetic material has a thickness of from about 100 nanometers toabout 10 micrometers and a magnetic shielding factor of at least about0.5; and said film of nanomagnetic material is disposed above at leastabout 50 percent of said first surface exposed to electromagneticradiation; (c) said nanomagnetic material has a mass density of at leastabout 0.01 grams per cubic centimeter, a saturation magnetization offrom about 1 to about 36,000 Gauss, a coercive force of from about 0.01to about 5,000 Oersteds, a relative magnetic permeability of from about1 to about 500,000, and an average particle size of less than about 100nanometers.
 2. The conductor assembly as recited in claim 1, whereinsaid nanomagnetic material has a saturation magnetizatioin of from about200 to about 26,000 Gauss.
 3. The conductor assembly as recited in claim1, wherein said nanomagnetic material has a coercive force of from about0.01 about 3,000 Oersteds.
 4. The conductor assembly as recited in claim1, wherein said nanomagnetic material has a relative magneticpermeability of from about 1.5 to about 260,000.
 5. The conductorassembly as recited in claim 1, wherein said nanomagnetic material has amass density of at least about 1 gram per cubic centimeter.
 6. Theconductor assembly as recited in claim 1, wherein said nanomagneticmaterial has a mass density of at least about 4 grams per cubiccentimeter.
 7. The conductor assembly as recited in claim 1, whereinsaid film of nanomagnetic material is disposed around said conductor. 8.The conductor assembly as recited in claim 1, wherein said film ofnanomagnetic material is contiguous with said conductor.
 9. Theconductor assembly as recited in claim 1, wherein said conductor iscomprised of a top surface and a bottom surface.
 10. The conductorassembly as recited in claim 9, wherein said nanomagnetic material iscontiguous with said top surface of said conductor.
 11. The conductorassembly as recited in claim 10, wherein said nanomagnetic material iscontiguous with said bottom surface of said conductor.
 12. The conductorassembly as recited in claim 9, wherein a first layer of insulatingmaterial is contiguous with said top surface of said conductor.
 13. Theconductor assembly as recited in claim 12, wherein a first layer ofnanomagnetic material is contiguous with said layer of insulatingmaterial.
 14. The conductor assembly as recited in claim 12, wherein asecond layer of insulating material is contiguous with said bottomsurface of said conductor.
 15. The conductor assembly as recited inclaim 14, wherein a second layer of nanomagnetic material is contiguouswith said second layer of insulating material.
 16. The conductorassembly as recited in claim 1, wherein said conductor is a cylindricalconductor.
 17. The conductor assembly as recited in claim 16, wherein ahelical member is disposed within said cylindrical conductor.
 18. Theconductor assembly as recited in claim 17, wherein said helical memberis coated with said nanomagnetic material.
 19. The conductor assembly asrecited in claim 1, wherein said nanomagnetic material is comprised offirst nanomagnetic composition and a second nanomagnetic composition.20. The conductor assembly as recited in claim 19, wherein said firstnanomagnetic composition has a particle size distribution that differsfrom said second nanomagnetic composition.
 21. The conductor assembly asrecited in claim 19, wherein said conductor is a cylindrical conductor.22. The conductor assembly as recited in claim 1, further comprisingmeans for cooling said conductor assembly.
 23. The conductor assembly asrecited in claim 22, wherein said means for cooling said conductorassembly is comprised of means for circulating fluid.
 24. The conductorassembly as recited in claim 1, further comprising a catheter tube and alumen comprised of an interior wall and an exterior wall.
 25. Theconductor assembly as recited in claim 24, wherein said nanomagneticmaterial is contiguous with said interior wall of said lumen.
 26. Theconductor assembly as recited in claim 24, wherein said nanomagneticmaterial is contiguous with said exterior wall of said lumen.
 27. Theconductor assembly as recited in claim 1, further comprising a catheterassembly comprised of an elongated tube and an axial lumen disposedwithin said elongated tube.
 28. The conductor assembly as recited inclaim 27, wherein said catheter assembly is flexible.
 29. The conductorassembly as recited in claim 27, wherein said catheter assembly iscomprised a layer of said nanomagnetic material contiguous with theouter wall of said elongated tube.
 30. The conductor assembly as recitedin claim 27, wherein said catheter assembly is comprised of a layer ofsaid nanomagnetic material contiguous with the inner wall of saidelongated tube.
 31. The conductor assembly as recited in claim 1,further comprising a guide wire device.
 32. The conductor assembly asrecited in claim 31, wherein said guide wire device is comprised of acoiled guide wire.
 33. The conductor assembly as recited in claim 32,wherein said guide wire device is comprised of a central support wire.34. The conductor assembly as recited in claim 33, wherein said guidewire device is comprised of a hemispherically shaped tip.
 35. Theconductor assembly as recited in claim 33, wherein said nanomagneticmaterial is contiguous with said coiled guide wire.
 36. The conductorassembly as recited in claim 33, wherein said nanomagnetic material iscontiguous with said central support wire.
 37. The conductor assembly asrecited in claim 1, further comprising a stent.
 38. The conductorassembly as recited in claim 37, wherein said stent is a self-expandingstent.
 39. The conductor assembly as recited in claim 38, wherein saidstent is comprised of a flexible film.
 40. The conductor assembly asrecited in claim 39, wherein said nanomagnetic material is contiguouswith said flexible film.
 41. The conductor assembly as recited in claim1, further comprising a biopsy probe assembly.
 42. The conductorassembly as recited in claim 41, wherein said biopsy probe assembly iscomprised of a hollow tubular cannula and a solid stylus.
 43. Theconductor assembly as recited in claim 42, wherein said biopsy probeassembly is comprised of stainless steel.
 44. The conductor assembly asrecited in claim 43, wherein said hollow tubular cannular is coated withsaid nanomagnetic material.
 45. The conductor assembly as recited inclaim 1, further comprising a flexible tube endoscope comprised of aflexible tube with a distally positioned objective lens.
 46. Theconductor assembly as recited in claim 45, wherein said flexible tubeendoscope further comprises a sheath disposed over said endoscope. 47.The conductor assembly as recited in claim 46, wherein said sheath iscoated with said nanomagnetic material.
 48. The conductor assembly asrecited in claim 1, wherein said conductor assembly is implantable. 49.The implantable conductor assembly as recited in claim 48, wherein saidconductor is a conductive coil coated with said nanomagnetic material.50. The implantable conductor assembly as recited in claim 48, whereinsaid conductor is a catheter coated with said nanomagnetic material. 51.The implantable conductor assembly as recited in claim 48, wherein saidconductor is a guide wire coated with said nanomagnetic material. 52.The implantable conductor assembly as recited in claim 48, wherein saidconductor is a stent coated with said nanomagnetic material.
 53. Theimplantable conductor assembly as recited in claim 48, wherein saidconductor is a biopsy probe coated with said nanomagnetic material. 54.The implantable conductor assembly as recited in claim 48, wherein saidconductor is an endoscope coated with said nanomagnetic material. 55.The implantable conductor assembly as recited in claim 48, wherein saidconductor is a sheath coated with said nanomagnetic material.